Electrical bushings are generally used with electrical distribution equipment, such as a transformer having a transformer housing which may be filled with oil and a transformer coil unit located with the transformer housing. Generally, electrical bushings include a bushing body affixable to a wall of a housing for the electrical distribution equipment, and an electrical conductor secured to the bushing body to be rigidly affixed with the bushing body. One end of the electrical conductor is located inside the housing to be connected by a suitable lead to internal electrical components, such as a transformer coil unit. The other end of the electrical conductor is generally located outside the housing to be disposed for interconnection with an electrical line for electrical equipment located externally of the housing.
Electrical bushings generally are of either a male type or female type, with the female type electrical bushing having a hollow interior portion adapted to receive a male electrical terminal for interconnection to external electrical equipment. Electrical bushings of the female type are often referred to as bushing wells.
Conversely, male electrical bushings are not provided with connector terminals recessed within a well but generally the bushing and terminal project from the wall of a housing.
Electrical bushings used with power distribution equipment of various types such as transformers, switchgear, switches and the like have always been susceptible to damage during handling, shipping, installation and maintainance operations. In order to minimize the likelihood of damage and to provide an economical electrical bushing for transformer applications which reduces the possibility of transformer oil leaking from the transformer housing around the electrical bushing, electrical bushings have been permanently mounted, as by welding, to the transformer wall. Such permanent mounting provides a sealed feedthrough connection for interconnecting the transformer unit to the electrical equipment located outside the transformer housing and also provides a secure mounting for the electrical bushing on the transformer wall.
While permanently mounting electrical bushings has prolonged the life of these bushings, the breakage and damage problem is still a substantial one. Bushing terminal breakage or damage typically occurs in the field during installation of a transformer, or similar power distribution equipment, and normally, damaged bushings cannot be properly replaced in the field. This means that the entire unit must often be returned for repair.
If a damaged electrical bushing is cut from a transformer in the field, access to the interior of the transformer housing must be attained to electrically connect a newly installed bushing. Furthermore, the process used to permanently mount the new electrical bushing on the transformer wall may occasionally not completely seal the transformer housing to the electrical bushing. A leakage problem will thereby be created, and such leakage may not be detected until the final stages of mounting the electrical bushing.
Removably mounted electrical bushings have been developed to facilitate the repair or replacement of damaged bushing components in the field. Such removable bushings are disclosed by U.S. Pat. Nos. 3,790,698 to F. O. Engert; 3,803,523 to D. J. Farmer et al and 3,909,509 to J. L. Fisher. These prior art bushing assemblies may be easily removed from a transformer wall in the field for repair or replacement without requiring that the bushing be cut from the transformer. However, for the repair of a relatively small bushing component, such as a broken terminal stud, the entire bushing must be removed. This often requires new electrical connections to be made with internal transformer components, and if the new bushing is not carefully sealed when it is mounted on the transformer wall, the likelihood of leakage around the bushing will be increased.
Since the terminal stud of an electrical bushing is the small component most likely to be damaged in the field, a need has arisen for a bushing construction wherein the terminal stud may be easily removed and replaced in the field without requiring the removal of the bushing from the housing of a power distribution unit.